Field of the Invention
The invention relates to an optical module of a micro spectrometer with a tapered slit and a slit structure thereof, and more particularly to a tapered slit formed by way of wet etching to serve as an element of an optical module of a micro spectrometer, and a slit structure of the micro spectrometer.
Related Art
A spectrometer is usually utilized to perform the measurement of the photometry of a radiation source, and a slit structure has to be used at a light entrance of the spectrometer to control a quantitative amount of light to enter the spectrometer. A slit with a very smooth and sharp opening has an important effect on the image quality and the resolution at the sensor end. Optically, the edge of this very smooth and sharp opening is referred to as a “knife edge.” However, because the opening of the slit of the conventional spectrometer has to be relatively long to permit the sufficient light input amount, the slit formed by semiconductor manufacturing processes using a substrate made of a silicon material or another semiconductor material appears to be very fragile and inadequate. Thus, the slit structure used in the conventional spectrometer is typically manufactured from a non-semiconductor material by way of electrical discharge machining (EDM). FIGS. 1 and 2 are a front view and a top view respectively showing a conventional slit structure 300. As shown in FIG. 2, a slit 310 of the slit structure 300 is manufactured by way of EDM, so its surface flatness is poor and has many sawtooth-like patterns. These sawtooth-like patterns may affect the incident light and cause the negative influence on the efficiency of the spectrometer. In addition, the electrical discharge machining (EDM) spends the higher cost and is not suitable for the mass production.
FIG. 3 is a schematic illustration showing a conventional spectrometer 100. Referring to FIG. 3, the conventional spectrometer 100 includes a light source 110, an input section 120, a collimator 130, a plane grating 140, a focus mirror 150 and a linear photosensor 160. The light source 110 outputs an optical signal 200, which passes through the input section 120 and the collimator 130 in the free space and then reaches the plane grating 140. A diffraction pattern 142 of the plane grating 140 has a plane macroscopic profile. Such a plane grating 140 is more suitable for the conventional machining method of ruling diffraction patterns on a metal surface using a diamond knife. However, the profile of the grating cannot be formed into a curved surface for providing the focus function using this machining method. Therefore, after the plane grating 140 separates the optical signal into several spectrum components, the focus mirror 150 has to be provided to focus these spectrum components onto the linear photosensor 160. As a result, the spectrometer 100 has the very long overall optical path, and the relatively large size. However, due to the optical module structure and the optical path of the conventional spectrometer, the light input amount of the conventional spectrometer may be very large, and the influence of the stray light on the diffraction result is relatively small. So, the problem of the influence of the stray light on the to-be-detected signal needs not to be considered in the conventional spectrometer, and the required smoothness of the slit 310 of the input section 120 is thus not high. As a result, the conventional slit structure manufactured by way of EDM still can be used, but is not adapted to the micro spectrometer, in which the light input amount is relatively small.